Context:
Sometimes what seem like good ideas in the rehearsal room don't work as well on stage as expected. Adjustments may be made at the technical rehearsal or even after the production has been in front of an audience during previews. Sometimes ideas are re-worked at a later stage when a production moves from Stratford to London.
In this production there is a large trap downstage centre which was sometimes lit with red flames to represent hell. Originally Macbeth was to fall through this in the final scene but the idea was cut after the first preview. It was still used for the witches to enter through and to produce smoke for the apparitions. There was also originally an idea that as Birnam wood moved towards the castle trees would be seen breaking through the stage floor.